In power tools, such as a circular saw or router, an internal electric motor has a rotating shaft coupled to a cutting tool at an exposed end. These cutting tools are selectively mounted to or removed from the shaft depending upon the work to be performed by the cutting tool. It is a convenience to the operator, if the rotation of the shaft can be inhibited during the mounting or removal of the cutting tool since the mounting or removal of the cutting tool requires a rotary motion about an axis concentric with the shaft. Preferably, the mechanism for locking the shaft should also inhibit electrical power from being applied to the electric motor when the rotation of the shaft is inhibited to prevent damage to the motor or causing it to overheat.
Shaft locking mechanisms which include electrical cut-out switches to prevent electrical power from being applied to the motor when the shaft is locked are known in the art. Godfrey et al, in U.S. Pat. No. 2,897,302, discloses a control mechanism for the ON/OFF switch of a router which automatically locks the shaft when the electrical switch is placed in the OFF position and release the shaft when the electrical switch is placed in the ON position. In an alternate arrangement disclosed by McCurry in U.S. patent application Ser. No. 07/764,239, filed Sep. 23, 1991, discloses a shaft lock mechanism having a first position in which the shaft is locked and a cut-out switch is placed in an open position and is manually displaceable to a second position in which the shaft is free to rotate and the cut-out switch is placed in a closed position.
The invention is an improved shaft lock mechanism for a power tool.